You can't be happy if you're just strong, even if you're the strongest exorcist in the world. Exorcist Haruyoshi Kuga, called an unrivaled genius, is betrayed by the Imperial Court and about to die. Resolving to be happy in his next life, he uses a secret reincarnation technique he created and reincarnates in another world. And so he receives a new name, Seika, and a new life. "What I lacked in my previous life was cunning. In this life, I'll be more calculating and find happiness." With the strongest exorcist techniques and strong demons working with him, what lies ahead for him? The peaceful life he wants, or.... This is the start of a story no one's ever seen before: the story of the strongest exorcist in a fantasy world.